The present invention refers to a mechanism for centering drawn hollow bodies in front of or above the die of a tool set consisting of a number of tools independent of one another, where each hollow body has a flared section in the edge zone of its open face.
In the non-cutting forming of metal hollow bodies which, for example, are employed for the production of tins or other metal containers, a circular blank stamped out of the original material is brought through a number of stages of shaping into the desired final shape of hollow body. The hollow-body blank designated in the description below as a semi-form is in that case conveyed by conveyor members, for example, grippers controlled in step with the press, from one shaping-station to another and shaped in stages. In that case, it is for the success of the shaping process of the highest importance that the semi-form gets centered, in front of or respectively above the die, i.e., shortly before the start of the shaping.
For certain reasons which are connected, e.g., with troublefree stripping of the semi-form from the punch and in particular are explained in the Swiss patent application No. 7570/73, it has proved advantageous to apply a flared section in the edge zone of the open face of the semi-form. The flared section in cylindrical semi-forms has essentially the shape of a flat truncated cone. As described in said Swiss Patent Application, the flared section at the top edge of the semi-form is applied deliberately in the course of shaping, in order to guarantee trouble free stripping of the semi-form from the ironing-punch in spite of extremely high stroke frequency and small thickness of wall. More recently, as shown in Swiss patent application No. 1977/72, stroke frequencies between 140 and 200 strokes per minute have become possible. The semi-forms are stretched to a wall thickness of about 0.1 mm. It now becomes clear that the special shape of the edge demands a special technical solution since the flared edge must under no circumstances get damaged or distorted.
The hollow bodies provided with a flared edge portion of the type described can no longer be centered by the conventional stationary centering ring. Otherwise, the flared section would collide with the centering ring arranged above or in front of the die and consequently be damaged. Centering mechanisms are indeed known in which spring-loaded centering members are forced away radially outwardly by the projecting and flared edge portion of the semi-form. Thus, the deflection motion of the centering members in that case is not effective forcibly, but only under the pressure of the flared edge portion itself encountering the centering members. This type of construction, therefore, can only be employed by fairly small, relatively compact semi-forms of about 16 to 20 mm diameter. That is, only this size of a flared edge portion can withstand the resilient prestressing of the centering members without permanent deformation.
For semi-forms of larger diameters and having extremely thin walls, very delicate hollow bodies are obtained by new methods of production. These known centering mechanisms are totally unusable. During their employment, deformation of the very flexible and thin walls of the hollow bodies cannot be avoided. Furthermore, the high stroke rate attendant the new methods of production could not be achieved when these known centering mechanisms were in use.